Tunnel diode



WITH s1:

Nov.-17, 1964 I I CONTROL SOURCE MODULA SOURCE INVEN 0R Hana/.0 Nan. oans's ATTORNEYS 1 Patented Nov. 17, 1964 cc, a substantial amount of power quency is required to operate a logical sisting of interconnected parametrons. t of the invention to provide an improved ploying active elements, which operates nic of a driving frequency. o the invention an electrical logic circuit es pair of active circuit elements adapted crating region of negative resistance, a tance elements of one sign connected T series pair of active elements, a

1 Filed Feb. 28,1 7 Claims priority, application.

5 Claims." c

i This invention. forming logica} Many pulse forming logical operati tions. Such circuits v dynamic storage devices for and the like. It is difficult operation at frequencies when number ofthese connected to form lar v electronic computer. I I

T he difiiculties associatefi largely eliminated inrons. A variety of log: are described in an Digital Computing Oscillation f by August 1959, pages 1 consists of a tuned cir nit element, and which with a frequency appro quency of the tuned c' i a variation of'theno I of active elements and to the reactance elements, the three reming an effective tuned circuit, 0 the tuned circuit a sinusoidal ving a frequency substantially twice ency of said tuned circuit, means for voltage across the pair of active eleor deriving from said tuned circuit an 'hich is at said resonant frequency and er one of two phases relatively disd means for applying an input signal he active elements to determine the ill now be described, by way of erence to the accompanying drawing diagram of a. logic circuit employing cy source 1 applies a sinusoidal drivesistor 2 to a pair of tunnel diodes air of inductors 5 and 6 and a connected in parallel with the e capacitor 7 has a negligible cy of the driving Voltage so that substantially at zero R.F. po .C. voltage from a source 20 is point between a supply terminal 8 and .C. voltage is effectively applied across air of tunnel diodes via the inductors 5 capacitor 7 preventing the short circuiting 's pp yor 9 is connected between the junction of the rs Sand 6 and the junction of the two tunnel 4. The tunnel diodes are biased in the forharmonic oscillation starts.

Provision must be madefor condition to the otherif the element. Substantial ener and this makes it impra one phase condition to the come by periodically quenchin' wave modulation of the excitin a small control voltage to dete' oscillation each time that it re-star'ts Although the parametron is wave device, the necessit r troduces the-difiiculty of o associated with pulse 0' monic oscillation takes an and decay, since the circuit consr elements. For example, twenty cycle; voltage may be required forrth build up to a uniform an mic the voltage to decay. A v number of'cycles at .u quired to provide an in ati cuit. Thus, the maximum to be only a sixtieth, or less, Furthermore, all the outpu the exciting source, since; th

therefore have a relatively low resistance, 50 ohms, for example. The tunnel diodes R.F. source 1 may typically operate at a of 250 mc./s. At this frequency, the reactance s. Since the reactances of the shunt capacities of the capacitor 7 are relatively small, an approxi- R.F. equivalent circuit is that of the two inductors 6 connected in parallel across the capacitor 9.

ned by the value of the capacitor 9 and the reductance of the two inductors in parallel. The he capacitor 9 and the inductors 5 and 6 are hat the resonant frequency is substantially the frequency of the driving voltage.

' nt of opposite sign connected to by the DC. voltage applied to the terbstantial shunt capacity of, for example,

t capacity of the tunnel diode is approximately 1 o inductors 5 and 6 and the capacitor 9 therefore effective tuned circuit with a resonant frequency The voltage/current characteristic of a tunnel diode is essentially N-shaped. At low voltages the diode behaves as a positive resistance of the order of 50 ohms, the current increasing fairly linearly to a peak of milliamperes at 0.1 volt. As the voltage is further increased, the diode enters a negative resistance region until the current has fallen to a minimum of about .75 milliampere at 0.45 volt. A second positive resistance region follows, so that a voltage of 0.6 volt again produces a current of 5 milliamperes.

It will be appreciated that these numerical values relate to a particular type of tunnel diode and that other type of tunnel diode will have difierent relative values of current and voltage, but that the general form of their voltage/current characteristic is the same.

It is a feature of devices possessing this N-shaped characteristic that they may be switched very rapidly from a point in the first positive resistance region to a corresponding point of equal current in the second positive resistance region, and vice versa. The RF. driving voltage controls this switching in the present circuit. As the voltage across the pair of tunnel diodes increases from the start of the first positive half-cycle of the driving voltage, it reaches a value suflicient to maintain one diode in the second positive resistance region and the other in the first positive resistance region. Assume that the diode 3 switches to the second region, then both diodes may be passing approximately 5 milliamperes, but the voltage across the diode 3 will be 0.6 volt and that across the diode 4 will be 0.1 volt. Prior to this, the voltage was divided equally between the two diodes, if they have similar characteristics. The driving voltage will reach a maximum and will then fall towards zero. As the drive voltage decreases, it will fall below the value necessary to maintain the diode 3 in the second region. Thus, the positive half cycle of the driving voltage will produce a positive going voltage pulse across the diode 3 and a negative going voltage pulse across the diode 4. These voltage pulses shock excite the effective tuned circuit, formed by the inductors 5 and 6 and the capacitor 9, at its natural resonant frequency. The negative half cycle of the driving voltage opposes the DC. voltage applied to the diodes from terminal 3, so that the diodes are not switched. During the next positive half cycle, the driving voltage will again be sufiicient to cause switching of the diodes. However, the tuned circuit was shock excited during the previous positive half cycle, so that current is still flowing in the tuned circuit. The current flows in opposite directions in the two inductors and the directions are such that a larger net positive voltage appears across the diode 4 than across the diode 3. Consequently, the diode 4 switches to the second region when the driving voltage increases to a sutiicient value. The current in the tuned circuit will have reversed when the next positive half cycle of the driving voltage occurs so that the diode 3 will switch. The diodes will continue to switch alternately on the positive half cycles of the driving voltage as long as the driving voltage is maintained, and the tuned circuit will be driven at the sub-harmonic frequency.

A balanced coupling to the tuned circuit is provided by coils 10 and 11 which are coupled to the inductors 5 and 6, respectively. The coils 10 and 11 are connected so that the induced voltages are additive and a sub-harmonic output voltage will be available at terminal 12 as long as the tuned circuit is driven. The phase of this output will be determined by which of the two positive resistance regions each of the diodes 3 and 4 adapts during the first positive cycle of the driving voltage, i.e., the output voltage will be either in one phase, or in an opposite phase, and once a particular mode is established 1t 15 self-sustaining. The phase of the output may therefore be determined by applying a small control voltage to the )llIlCtlOIl of the two tunnel diodes, to unbalance the voltages across them, during the initial application of the driving voltage. The control voltage may be a sub-harmonic output derived from another similar logic circuit which is applied to an input terminal 13, and is fed to the junction by a coupling capacitor 14. The output coils, such as the coils 10a, 11a, and 10b, 11b, of other logic circuits may be connected in series and to the terminal 13. The majority of signals which have a common phase will then cause the circuit to lock to that phase. A DC. signal from a control source 21, which may be the output from a resistor majority logic circuit, may be applied directly to the junction of the diodes as a control signal, the polarity of the signal determining which diode is switched first.

The driving frequency source 1 may be modulated by a square wave from a modulation source 22 to allow the control signals to be effective, in a similar manner to a parametron. A chain of the tunnel diode logic circuits may be operated by using two or three driving sources with different phases for the modulation frequency, successive circuits being driven from different phases.

The control voltages may also be made eliective by sine wave modulation of the driving source 1. This is possible because of a hysteresis effect in the switching characteristic. In order to switch the circuit from a quiescent state to a locked phase state, the voltage across one of the tunnel diodes consisting of the sum of the DC. voltage across that diode, due to the source 20, the voltage from the driving source 1 and any applied control voltage, must exceed the switching voltage of that diode. However, once the circuit is.in the locked phase state, the sub-harmonic voltage is also present and it is always adding to the other voltages across that diode which is switched. Consequently, once the circuit is operating in the locked phase state, the amplitude of driving voltage necessary to keep it operating is smaller than is the amplitude needed to switch it. The operating conditions may be selected so that the mean operating point of the diodes lies between the switching and maintaining voltages, then less than percent sine wave modulation of the driving voltage provides sufiicient voltage variation to switch the circuit alternately between the quiescent and locked phase states.

It will be apparent that the R.F. driving source 1 acts primarily as a switching voltage source which controls the relative distribution of the applied D.C. voltage be tween the two tunnel diodes. Consequently, a. substantial part of the output power, which is available at'terminal 12, is drawn from the DC. source. This greatly reduces the power required from the R.F. source to provide a given output power. This is a major advantage, since the generation of power at frequencies of the order of 250 mc./s., and upward is at a low efiiciency. The design requirements of the driving source are also less stringent if sine wave modulation rather than square wave modulation is used.

However, the main advantage obtained by the inclusion of active circuit elements, in the form of tunnel diodes, is the great increase in switching speed as compared with the conventional parametric circuit. The voltage appearing across the diodes when they are switched is determined by the diode characteristics. Consequently, the rise time is set simply by the time required for the amplitude of the sub-harmonic oscillation in the tuned circuit to stabilise with constant amplitude pulses applied to it. Correspondingly, the fall time is set by the rate at which the energy stored in the tuned circuit can be dissipated by the active elements. Thus, it is possible to achieve a complete switching cycle in, say, ten cycles of the driving waveform.

The circuit which has been described may be considered as having two stable states, since the single output may have either of two phases. It is possible to construct multi-stable arrangements in which multiple outputs are diode A c regions and a negative re- 6 circuit, including a series circuit ected pair of similar two terrangement em ected in the same sense for will be consi series circuit and exhibiting, d voltage, first and second formed'by the inductors,

in series m 11 said positive resistance pair circiit I u said active elements; a the diode s connected across said The two between said inductors; a diode pair said first and second junceither phasema d inductors together forming output with either phase apply a uni-directional voltage circuit cted pair of active elements;

It will be ap 'd serially-connected pair of acconvenient I g driving signal having a freductor. In this form,

tion between said first I output the resonant frequency of the factureland tive elements to switch re tween said first and second means to produce an output e switching of the active eleat said resonant frequency 'f two phases which are relad control means to apply to signal to select the phase of other devices, whi a generally similar to with a negative resistelm The function of capacitor the desir may equal] well be} by it g uit, including a series circuit r ted pair of similar tunnel th i d ile sense for current flow I claim} I h diode exhibiting a cur- 1, A el t i l 1 g-first and second positive comprising e resistance region bei l qivg ons; a first junction 'h i "ply a uni-directional gionsgepa a I v I bias each diode in the elements be'mg 7 Of inductors connected fl thrd h Said 3 '5 "second junction between said s id ti 1e em connected between said first and e t connected aqrdgg said inductors and said capacitor toya tuned circuit; means to apply across es an alternating driving voltage, having antially twice the resonant frequency of to cause the diodes to switch repeatedly v betweensaid first and second positive "means to produce an output signal in switching of the diodes, said output resonant frequency and having, selecbases which are relatively displaced,

means to apply to said first junction select the phase of said output signal. cal logic circuit, including a serially-con vf similar tunnel diodes each having first and -1 ctrodes, the first electrode of one diode being ed to the second electrode of the other diode at junction; a series pair of inductors coupled to said jof diodes; a second junction between the inductors of i'pair; a capacitor connected between said first and junctions, said pair of inductors and said capacito forming a tuned circuit; means to apply, by way: r of inductors, a voltage across the pair of bias each diode to substantially the same operatt, each diode exhibiting a current/voltage charhaving first and second positive resistance rea negative resistance region between said tance regions; means to apply across saidalternating voltage of frequency subresonant frequency of said tuned 'odes to switch repeatedly in opposite first and second positive resistance 1 output Sign al which oscillations in the tuned circuit; -a which has selectively d to said pair of inductors to protively displaced y ponse to said oscillations, said i l to id fi t yone of two phases depending the diodes switch to said first actance elementconnect junctions, said first and second forming a tuned circuit; means to appl fa voltage across said serially-connect ments; means to apply across said an alternating driving voltage tially twice the resonant 0 means to derive from which is at said resonant tively, one or two 180; and means to'appl H signal to select the phase 2. An electrical logic cf cuit comprising a serially-co I terminal active circuit elementsexln of current against applied'voltap second positive resistance regions resistance region, said active cl the same sense for current flow, I a first junction betweensaid'acjti of inductors connected acrossisai junction between the inductor-so connected between. said first and capacitor and saidinduc circuit; meanstoapp said serially-connected;v apply across driving voltage havm resonant frequency" 'f' ductor coupled tohaid positive resistance region; modulating means to modulate said alternating voltage to quench and restart said oscillations; and control means to select the phase of said output signals by applying to said first junction a signal to control said sequence.

References Cited in the file of this patent UNITED STATES PATENTS 3,056,039 Onyshkevych et a1 Sept. 25, 1962 3,084,264 Kosonocky et a1 Apr. 2, 1963 OTHER REFERENCES Pub. 1, International Solid State Ckts. Conf., Digest of Tech. Papers, Parametron and Esaki Diode Progress in Japan, by Goto, pages 20 and 21, February 15, 1961.

Pub. II (Digest as above), Parametric Oscillation and Amplification Using Esaki Diodes, pages 28 and 29,

Kreer Oct. 14, 1952 10 February 15, 1961. 

1. AN ELECTRICAL LOGIC CIRCUIT, INCLUDING A SERIES CIRCUIT COMPRISING A SERIALLY-CONNECTED PAIR OF SIMILAR TWO TERMINAL ACTIVE CIRCUIT ELEMENTS EXHIBITING AN OPERATING CHARACTERISTIC HAVING FIRST AND SECOND POSITIVE RESISTANCE REGIONS SEPARATED BY A NEGATIVE RESISTANCE REGION, SAID ACTIVE ELEMENTS BEING CONNECTED IN THE SAME SENSE FOR CURRENT FLOW THROUGH SAID SERIES CIRCUIT; A FIRST JUNCTION BETWEEN SAID ACTIVE ELEMENTS; A SERIES PAIR OF FIRST REACTANCE ELEMENTS CONNECTED ACROSS SAID SERIES CIRCUIT; A SECOND JUNCTION BETWEEN SAID FIRST REACTANCE ELEMENTS; A SECOND REACTANCE ELEMENT CONNECTED BETWEEN SAID FIRST AND SECOND JUNCTIONS, SAID FIRST AND SECOND REACTANCE ELEMENTS TOGHTHER FORMING A TUNED CIRCUIT; MEANS TO APPLY A UNI-DIRECTIONAL VOLTAGE ACROSS SAID SERIALLY-CONNECTED PAIR OF ACTIVE ELEMENTS; MEANS TO APPLY ACROSS SAID PAIR OF ACTIVE ELEMENTS AN ALTERNATING DRIVING VOLTAGE HAVING A FREQUENCY SUBSTANTIALLY TWICE THE RESONANT FREQUENCY OF SAID TUNED CIRCUIT; MEANS TO DERIVE FROM SAID TUNED CIRCUIT AN OUTPUT SIGNAL WHICH IS AT SAID RESONANT FREQUENCY AND WHICH HAS, SELECTIVELY, ONE OR TWO PHASES WHICH ARE RELATIVELY DISPLACED BY 180*; AND MEANS TO APPLY TO SAID FIRST JUNCTION A CONTROL SIGNAL TO SELECT THE PHASE OF SAID OUTPUT SIGNAL. 